A next generation standard of the common interface plus (CI+) in digital video broadcasting (DVB), which is being operated mainly in Europe, is now under review. The conventional CI+ is used to prevent illicit outflow of broadcast content by performing mutual authentication and protection of a communication channel between a host (mainly a TV set) and a conditional access module (CAM). Development of a standard for the next generation CI+ is under way, and communication system content is also reviewed as a scope of protection targets. Generally, the communication system content is protected by the digital rights management (DRM) technology.
The DRM technology can protect a communication channel between a server and a client against illicit behavior such as eavesdropping (wiretapping) or falsification of content. On the one hand, since content outputted from a receiver cannot be protected by the DRM, a digital watermark technology is generally used as means of detecting unauthorized copying or falsification of content after the content is outputted (see, for example, Patent literature 1 below).